fix(domain): cut confirmation false positives via weak subscribe signal

A "manage subscription" / "subscribe" footer link is now a weak (+1) URL
signal instead of strong (+2), so an ordinary newsletter with a stray body
keyword (active/valid) no longer crosses the detection threshold. A genuine
"confirm your subscription" subject + a bare /subscribe link still passes.
Also dedupe surfaced links. Adds false-positive + recall + dedupe tests.

src/domain/confirmation.test.ts

@@ -95,4 +95,79 @@ describe("detectConfirmation", () => {
     });
     expect(result).toBeNull();
   });
+
+  // ── False-positive guards: ordinary newsletters must NOT be flagged ──────────
+  // A "manage subscription" footer link is only a weak signal (+1), so a stray
+  // body keyword (active/valid) cannot push it over the threshold.
+
+  it("does not flag a newsletter with a manage-subscription footer + 'active' in body", () => {
+    const result = detectConfirmation({
+      subject: "This week in tech",
+      text: "Thanks to our most active community members for the great discussion.",
+      links: [
+        { href: "https://news.example.com/article/42", text: "Read more" },
+        {
+          href: "https://news.example.com/account/subscription",
+          text: "Manage your subscription",
+        },
+      ],
+    });
+    expect(result).toBeNull();
+  });
+
+  it("does not flag a newsletter with a subscription-preferences link + 'valid' in body", () => {
+    const result = detectConfirmation({
+      subject: "Weekend deals are here",
+      text: "These offers are valid until Friday — don't miss out.",
+      links: [
+        {
+          href: "https://shop.example.com/subscription/preferences",
+          text: "Subscription preferences",
+        },
+      ],
+    });
+    expect(result).toBeNull();
+  });
+
+  it("does not flag a marketing 'Subscribe & save' CTA + 'activate' in body", () => {
+    const result = detectConfirmation({
+      subject: "Your weekly digest",
+      text: "Activate your free trial and start saving today.",
+      links: [
+        {
+          href: "https://shop.example.com/subscribe",
+          text: "Subscribe & save",
+        },
+      ],
+    });
+    expect(result).toBeNull();
+  });
+
+  // ── Recall: a genuine confirmation still passes via the weak signal ──────────
+  it("detects a genuine confirm-subscription email whose only link is a bare /subscribe", () => {
+    const result = detectConfirmation({
+      subject: "Please confirm your subscription",
+      text: "Tap the button to finish signing up.",
+      links: [
+        {
+          href: "https://news.example.com/subscribe/abc123",
+          text: "Subscribe",
+        },
+      ],
+    });
+    expect(result).not.toBeNull();
+    expect(result![0]).toBe("https://news.example.com/subscribe/abc123");
+  });
+
+  it("dedupes a confirmation link repeated in the body", () => {
+    const result = detectConfirmation({
+      subject: "Confirm your subscription",
+      text: "verify your address",
+      links: [
+        { href: "https://x.example/confirm?token=1", text: "Confirm" },
+        { href: "https://x.example/confirm?token=1", text: "Confirm here" },
+      ],
+    });
+    expect(result).toEqual(["https://x.example/confirm?token=1"]);
+  });
 });

src/domain/confirmation.ts

@@ -29,8 +29,9 @@ const KEYWORDS = [
   "optin",
 ];
 
-// Link URL/anchor signals (normalized). A link matching any → candidate.
-const LINK_SIGNALS = [
+// Strong URL signals: an unambiguous confirm/verify/activate action or a token.
+// A link URL matching any scores +2.
+const STRONG_LINK_SIGNALS = [
   "confirm",
   "verif",
   "activ",
@@ -40,13 +41,17 @@ const LINK_SIGNALS = [
   "optin",
   "opt-in",
   "double-optin",
-  "subscription",
-  "subscribe",
   "token=",
   "confirm=",
   "activation",
 ];
 
+// Weak URL signals: ambiguous subscribe/subscription words that also appear in
+// ordinary "manage subscription" footers. Worth only +1 so they cannot, on their
+// own (with a stray body keyword), cross the threshold and cry wolf — but still
+// let a genuine "confirm your subscription" subject + a bare /subscribe link pass.
+const WEAK_LINK_SIGNALS = ["subscription", "subscribe"];
+
 // Negative patterns: a link matching any of these is NEVER a candidate, and these
 // tokens are stripped from text before keyword scanning (kills the unsubscribe
 // false positive — "unsubscribe" contains "subscribe").
@@ -79,7 +84,8 @@ function linkScore(href: string, text: string): number {
   const t = normalize(text);
   if (matchesAny(h, NEGATIVE) || matchesAny(t, NEGATIVE)) return 0;
   let score = 0;
-  if (matchesAny(h, LINK_SIGNALS)) score += 2;
+  if (matchesAny(h, STRONG_LINK_SIGNALS)) score += 2;
+  else if (matchesAny(h, WEAK_LINK_SIGNALS)) score += 1;
   if (matchesAny(t, KEYWORDS)) score += 2;
   return score;
 }
@@ -110,5 +116,7 @@ export function detectConfirmation(
 
   if (subjectScore + bodyScore + bestLinkScore < THRESHOLD) return null;
 
-  return candidates.slice(0, 3).map((c) => c.href);
+  // Dedupe by href before capping, so a link repeated in the body never wastes
+  // one of the three surfaced slots.
+  return [...new Set(candidates.map((c) => c.href))].slice(0, 3);
 }